Cylindrical alkaline electrochemical cells generally comprise the following major internal components: anode, cathode, separator, electrolyte, a cylindrical cup shaped metallic container and a current collector assembly. The current collector assembly usually consists of two or more parts that are preassembled to form the current collector assembly which is then inserted into the open end of the container thereby sealing the electrochemically active components within the container. The current collector assembly generally comprises an elastomeric seal body with a centrally located opening and an electrically conductive current collector which is designed to provide electrical continuity from the exterior side of the seal body, through the seal body's opening to the interior of the cell. Although a variety of current collector designs may be used, many battery manufacturers use collectors that are shaped like a nail. This type of collector is generally an elongated rod with a head formed on one end and a point on the other end. The head is formed by flattening the end of the collector thereby increasing the diameter of the rod and creating a ledge or bulge. In conventional battery manufacturing processes, the current collector assembly is manufactured by inserting the pointed end of the collector through the exterior side of the seal body's centrally located opening and forcing the shaft of the collector through the seal body until the head of the collector abuts the exterior surface of the seal body. This process requires that the collector be oriented prior to insertion and that virtually the entire length of the collector pass through the opening in the seal.
A variation of this process which has been used to produce commercially available cells is to weld one end of a rod shaped current collector to the inside surface of a cell's exterior cover and then insert the opposite end of the collector through the seal's central opening until the inside surface of the cover abuts the outside surface of the seal body. This process produces a cell with a rod shaped collector inserted through a seal body.
U.S. Pat. No. 4,606,983 discloses a terminal conductor which incorporates an anchoring means, such as a rounded barb functioning as a buttress, to prevent extraction or explusion of the conductor from the cell. During the cell assembly process, the pointed end of the conductor is inserted into the seal's central opening so that the shank of the collector is forced through the seal body's external opening until the head of the nail abuts the outside surface of the seal.
U.S. Pat. No. 1,650,319 discloses a current collector for batteries which contain manganese dioxide within a cup shaped zinc container. The centrally located current collector has a constant diameter throughout most of its length. However, at one end, a short section of the collector has a reduced diameter and that portion of the collector is inserted through the opening in the sealing disc until the shoulder of the collector abuts the interior surface of the sealing disc.
The prior art processes for manufacturing current collector assemblies have the following disadvantages. First, the collectors must be oriented prior to insertion of the collector through the seal. Second, one of the long standing problems with this type of process is the sensitivity of the collector assembly process to misalignment of the collector during insertion which may allow the leading end of the collector to nick or scratch the interior surface of the seal's opening. Third, small imperfections on the surface of the collector's shaft can create longitudinal grooves in the seal body as the collector is inserted through the seal's opening. The resulting nicks, scratches or grooves in the seal may enable the cell's electrolyte to migrate via the groove from inside the cell to outside the cell. In order to prevent leakage of electrolyte from the cell along the surface of the nail's shaft, battery manufacturers that use a nail shaped current collector have been forced to spend substantial amounts of money to develop and monitor current collector manufacturing processes that do not mar the surface of the collector prior to inserting the collector through the seal. In addition, battery manufacturers must insure that the collector assembly manufacturing processes maintain virtually perfect alignment between the nail and seal during insertion of the collector through the seal body in order to avoid the possibility of damaging the inner surface of the seal body's central opening. Fourth, collector shapes are generally limited to those shapes which can be easily inserted through a seal body. Conventionally, collectors with constant diameters are preferred. Nonsymmetrically shaped collectors, such as those which are curvilinear or have been flattened in order to increase the collector's surface area, have not been used because the nonsymmetrically shaped portion of the collector could not be forced through the opening in the seal body. Yet another problem with the known manufacturing processes is the time required to fabricate a current collector assembly. In high speed manufacturing processes, there is a need to reduce assembly time in order to minimize manufacturing costs. However, the known current collector assembly processes actually waste time when the longest portion of the collector is forced through the seal even though only a small portion of the collector needs to be inserted through the seal. While the manufacturing processes currently in use have been successful in producing large quantities of current collector assemblies, there is a need to develop a current collector assembly process that: (1) simplifies the manufacturing process by eliminating the need to orient a collector prior to insertion, (2) allows irregularly shaped collectors to be assembled into current collector assemblies, (3) decreases manufacturing costs by inserting a minimum length of the collector through the seal body thereby minimizing the time required to fabricate the current collector assembly, and (4) reduces the risk of leakage by minimizing the opportunity for damaging the inner surface of the seal's opening during the collector insertion process.